JPCA: La2@C72 and Sc2@C72: Computational Characterizations

J. Phys. Chem. A, ASAP Article 10.1021/jp055894u S1089-5639(05)05894-9
Web Release Date: January 26, 2006

Copyright © 2006 American Chemical Society

La₂@C₇₂ and Sc₂@C₇₂: Computational Characterizations

Zdenk Slanina,* Zhongfang Chen,* Paul v. R. Schleyer, Filip Uhlík, Xin Lu, and Shigeru Nagase

Abstract:

The La₂@C₇₂ and Sc₂@C₇₂ metallofullerenes have been characterized by systematic density functional computations. On the basis of the most stable geometry of 39 C₇₂ hexaanions and the computed energies of the best endofullerene candidates, the experimentally isolated La₂@C₇₂ species was assigned the structure coded #10611. The good agreement between the computed and the experimental ¹³C chemical shifts for La₂@C₇₂ further supports the literature assignment (Kato, H.; Taninaka, A.; Sugai, T.; Shinohara, H. J. Am. Chem. Soc. 2003, 125, 7782). The geometry, IR vibrational frequencies, and ¹³C chemical shifts of Sc₂@C₇₂ were predicted to assist its future experimental characterization.

JPCA: La2@C72 and Sc2@C72: Computational Characterizations

J. Phys. Chem. A, ASAP Article 10.1021/jp055894u S1089-5639(05)05894-9
Web Release Date: January 26, 2006

Copyright © 2006 American Chemical Society

La₂@C₇₂ and Sc₂@C₇₂: Computational Characterizations

Zdenk Slanina,* Zhongfang Chen,* Paul v. R. Schleyer, Filip Uhlík, Xin Lu, and Shigeru Nagase

Department of Theoretical Molecular Science, Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Aichi, Japan, Department of Chemistry and Center for Computational Chemistry, University of Georgia, Athens, Georgia 30602-2525, Department of Physical and Macromolecular Chemistry, School of Science, Charles University, 128 43 Prague 2, Czech Republic, and Department of Chemistry, Xiamen University, Xiamen 361005, China

Received: October 14, 2005

In Final Form: December 11, 2005

Abstract:

The La₂@C₇₂ and Sc₂@C₇₂ metallofullerenes have been characterized by systematic density functional computations. On the basis of the most stable geometry of 39 C₇₂ hexaanions and the computed energies of the best endofullerene candidates, the experimentally isolated La₂@C₇₂ species was assigned the structure coded #10611. The good agreement between the computed and the experimental ¹³C chemical shifts for La₂@C₇₂ further supports the literature assignment (Kato, H.; Taninaka, A.; Sugai, T.; Shinohara, H. J. Am. Chem. Soc. 2003, 125, 7782). The geometry, IR vibrational frequencies, and ¹³C chemical shifts of Sc₂@C₇₂ were predicted to assist its future experimental characterization.

Inorg. Chem., 44 (24), 8770 -8785, 2005. 10.1021/ic0510922 S0020-1669(05)01092-X Web Release Date: October 28, 2005

Syntheses; 77Se, 203Tl, and 205Tl NMR; and Theoretical Studies of the Tl2Se66-, Tl3Se65-, and Tl3Se75- Anions and the X-ray Crystal Structures of [2,2,2-crypt-Na]4[Tl4Se8]·en and [2,2,2-crypt-Na]2[Tl2Se4]1·en
Ayaaz M. Pirani, Hélène P. A. Mercier,* Reijo J. Suontamo, Gary J. Schrobilgen,* David P. Santry, and Horst Borrmann
Department of Chemistry, McMaster University, Hamilton, Ontario L8S 4M1, Canada, Department of Chemistry, University of Jyväskylä, P.O. Box 35, FIN-40014, Finland, and Max-Planck-Institut für Chemische Physik fester Stoffe, Raum B1.2.11, Nöthnitzer Strasse 40, Dresden D-01187, Germany

Abstract: The 2,2,2-crypt salts of the Tl4Se84- and [Tl2Se42- anions have been obtained by extraction of the ternary alloy NaTl0.5Se in ethylenediamine (en) in the presence of 2,2,2-crypt and 18-crown-6 followed by vapor-phase diffusion of THF into the en extract. The [2,2,2-crypt-Na]4[Tl4Se8]·en crystallizes in the monoclinic space group P21/n, with Z = 2 and a = 14.768(3) Å, b = 16.635(3) Å, c = 21.254(4) Å, = 94.17(3) at -123 C, and the [2,2,2-crypt-Na]2[Tl2Se4·en crystallizes in the monoclinic space group P21/c, with Z = 4 and a = 14.246(2) Å, b = 14.360(3) Å, c = 26.673(8) Å, = 99.87(3) at -123 C. The TlIII anions, Tl2Se66- and Tl3Se75-, and the mixed oxidation state TlI/TlIII anion, Tl3Se65-, have been obtained by extraction of NaTl0.5Se and NaTlSe in en, in the presence of 2,2,2-crypt and/or in liquid NH3, and have been characterized in solution by low-temperature 77Se, 203Tl, and 205Tl NMR spectroscopy. The 1J(203,205Tl-77Se) and 2J(203,205Tl-203,205Tl) couplings of the three anions have been used to arrive at their solution structures by detailed analyses and simulations of all spin multiplets that comprise the 205,203Tl NMR subspectra arising from natural abundance 205,203Tl and 77Se isotopomer distributions. The structure of Tl2Se66- is based on a Tl2Se2 ring in which each thallium is bonded to two exo-selenium atoms so that these thalliums are four-coordinate and possess a formal oxidation state of +3. The Tl4Se84- anion is formally derived from the Tl2Se66- anion by coordination of each pair of terminal Se atoms to the TlIII atom of a TlSe+ cation. The structure of the [Tl2Se42- anion is comprised of edge-sharing distorted TlSe4 tetrahedra that form infinite, one-dimensional [Tl2Se42- chains. The structures of Tl3Se65- and Tl3Se75- are derived from Tl4Se4-cubes in which one thallium atom has been removed and two and three exo-selenium atoms are bonded to thallium atoms, respectively, so that each is four-coordinate and possesses a formal oxidation state of +3 with the remaining three-coordinate thallium atom in the +1 oxidation state. Quantum mechanical calculations at the MP2 level of theory show that the Tl2Se66-, Tl3Se65-, Tl3Se75-, and Tl4Se84- anions exhibit true minima and display geometries that are in agreement with their experimental structures. Natural bond orbital and electron localization function analyses were utilized in describing the bonding in the present and previously published Tl/Se anions, and showed that the Tl2Se66-, Tl3Se65-, Tl3Se75-, and Tl4Se84- anions are electron-precise rings and cages.

Chem. Mater.; 2005; 17(26) pp 6545 - 6554; (Article) DOI: 10.1021/cm050396j

Characterization of BAPO- and SAPO-Based Mesoporous Materials by Solid-State NMR Spectroscopy Yining Huang, Zhimin Yan, and Roger Richerpp 6545 - 6554; (Article) DOI: 10.1021/cm050396j

Comment: Phosphor NMR!!!!!!

Abstract: We have utilized several heteronuclear dipolar-coupling based 27Al/31P, 31P/11B, 27Al/11B, 27Al/29Si, and 1H/31P double-resonance solid-state NMR techniques to characterize boroaluminophosphate (BAPO)- and silicoaluminophosphate (SAPO)-based mesoporous materials. For the hexagonal BAPO materials, the coordination geometry of the B atoms in the framework is exclusively tetrahedral. The fraction of B atoms that can be incorporated in the framework seems not to depend on the B content of the initial gel. For the vast majority of the framework B atoms, the coordination environment is B(-OP)4. The B-O-Al linkages, however, also exist. The results indicate that the four-coordinated B atoms are not distributed randomly within the framework. Instead, they appear to be located on the channel surface. For the SAPO-based mesophase, the connectivities between various P and Al sites were mapped and the chemical environments of different P sites were determined to be as follows: (HO)2P[OAl(oct)]2, (HO)P[OAl(tet)]x[OAl(oct)]3-x, and (HO)P[OAl(tet)]3. The Si-O-Al linkages were detected unambiguously.

Chem. Mater.; 2005; 17(22) pp 5481 - 5488; (Article) DOI: 10.1021/cm0513132

Formation of Porous Aluminophosphate Frameworks Monitored by Hyperpolarized 129Xe NMR Spectroscopy Devin N. Sears, Bryan A. Demko, Kristopher J. Ooms, Roderick E. Wasylishen, and Yining Huangpp 5481 - 5488; (Article) DOI: 10.1021/cm0513132

Abstract:
The formation of two aluminophosphate frameworks, AlPO4-5 and AlPO4-18, has been monitored using hyperpolarized 129Xe NMR as a probe. The reaction progress from an amorphous phase to AlPO4-5 and its subsequent conversion to AlPO4-18 is observed for xenon adsorbed in samples that have been reacted for varying lengths of time. The extreme sensitivity of 129Xe chemical shifts to local environments of the xenon leads to separate NMR peaks for xenon adsorbed in the two different aluminophosphate frameworks present in a single reaction mixture. For xenon adsorbed in AlPO4-5, an anisotropic 129Xe NMR line shape at iso 63 ppm is observed, whereas for xenon in AlPO4-18, a peak with a small anisotropy at iso 74 ppm is observed. Grand canonical Monte Carlo simulations provide a theoretical description of xenon adsorbed in the two aluminophosphate frameworks, and the resulting simulated 129Xe NMR line shapes are in good agreement with experimental data. Two-dimensional exchange NMR spectroscopy was used to examine the exchange of xenon between AlPO4-5, AlPO4-18, and bulk xenon gas. The results indicate that the domains of AlPO4-5 are in intimate contact with those of AlPO4-18, facilitating a higher intercrystallite exchange than with the bulk xenon gas.

Chem. Mater., 17 (22), 5428 -5438, 2005. 10.1021/cm050961i S0897-4756(05)00961-0 Web Release Date: September 29, 2005

Comment: Looks similar to the compounds you are working on Hiyam

Energetics of Self-Assembly and Chain Confinement in Silver Alkanethiolates: Enthalpy-Entropy Interplay
Andrey A. Levchenko, Chanel K. Yee, Atul N. Parikh, and Alexandra Navrotsky*
Thermochemistry Facility and NEAT ORU and Applied Science Department, University of California at Davis, Davis, California 95616

Abstract: The formation enthalpies by in situ direct synthesis calorimetry for a series of silver alkanethiolates, AgS(CH2)nCH3, with various long chain-length substituents (n = 9, 11, 15, and 17) are reported. The calorimetric results support a mechanism of stepwise hierarchical assembly involving primary directional interactions between Ag and S forming the inorganic core and secondary stacking facilitating the formation of the three-dimensional structure. The formation enthalpy data are chain-length dependent, indicating an energy of -4 ± 0.5 kJ/mol per methyl group due to alkyl chain interactions. The chain independent component of the enthalpy associated with bonding between Ag and S is -137 ± 6 kJ/mol, which is consistent with previous experimental data and ab initio calculations for these and related materials. A new recrystallization method offers significantly improved structural consistency across the chain-length series. Larger purified crystals, prepared by this method, were used to probe the structure, thermodynamics of phase transitions, and thermal stability, using a combination of differential scanning and solution calorimetry, thermogravimetric analysis, evolved gas Fourier transform infrared spectroscopy, and temperature-dependent X-ray diffraction. The DSC data show that the temperature of the main phase transition at 131 C is essentially independent of the length of the alkyl chain substituents for recrystallized samples. This chain-length independence does not reflect constant enthalpy of transition but rather a complex interplay between enthalpic and entropic contributions. In agreement with previous studies, this phase transition is assigned to a fully reversible transformation from the layered crystalline structure to a columnar mesophase, characterized by structural rearrangements of the inorganic framework and partial conformational disordering of the chain substituents. In situ scanning calorimetry in toluene upon slow heating from room temperature to 110 C, where the sample appeared to dissolve in the toluene near 100 C, gives insight into chain assembly and crystal growth. The second reaction seen in DSC at 210 C is an irreversible transformation to an amorphous derivative, ultimately leading to the formation of silver and silver sulfide crystals resulting from the chemical decomposition of alkyl chains.

Chem. Mater., 17 (22), 5411 -5419, 2005. 10.1021/cm050813s S0897-4756(05)00813-6 Web Release Date: October 4, 2005

Comment: Hiyam you may want to have a look at this paper. It appears to be similar to Shimizu's stuff.

Facile Synthesis and Highly Reactive Silver Ion Adsorption of Novel Microparticles of Sulfodiphenylamine and Diaminonaphthalene Copolymers
Xin-Gui Li,* Rui Liu, and Mei-Rong Huang*
Institute of Materials Chemistry, School of Materials Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China, and Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138
Received April 18, 2005
Revised Manuscript Received August 25, 2005

Abstract:
A series of novel copolymer microparticles from 4-sulfonic diphenylamine (SDP) and 1,8-diaminonaphthalene (DAN) was facilely prepared by a chemically oxidative polymerization. The structures and properties of the microparticles were systematically characterized by several important techniques. The microparticles exhibit good water resistance and high thermostability. Their electrical conductivity significantly rises after HCl doping or Ag adsorption. The Ag+ reactive adsorbability of the microparticles was optimized by carefully regulating the SDP/DAN ratio, particle size, and Ag+ solution pH. Both the introduction of SDP units into DAN polymer chains and the diminution of the particle size can effectively increase the capacity and rate of Ag+ adsorption. In particular, the Ag+ adsorbance on SDP/DAN (30/70) copolymer microparticles reaches 2.0 g g-1, which is the highest silver adsorption capacity reported thus far. A novel mechanism of Ag+ reactive adsorption on the microparticles containing a large number of reactive groups such as amino, imino, and sulfonic groups has been proposed. The microparticles could be very applicable to elimination and recovery of noble metallic ions in wastewater.

CPL: Ronald Dong: 13C tensors in mesogens, SUPER sequence

Nice extraction of 13C tensors in a complicated system.

Chemical Physics Letters
Volume 417, Issues 4-6 , 10 January 2006, Pages 475-479

On the carbon-13 chemical shift tensors of bent-core mesogens

Ronald Y. Dong a, b, J. Zhanga and K. Fodor-Csorbac

aDepartment of Physics and Astronomy, University of Manitoba, Winnipeg, Man., Canada R3T 2N2
bDepartment of Physics and Astronomy, Brandon University, Brandon, Man., Canada R7A 6A9
cResearch Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, 1525 Budapest, Hungary

Abstract

Solid state NMR techniques are used to study bent-shape achiral molecules which can form a new type of mesophases, known as ‘banana’ or B phases. In particular, a recent method called SUPER is applied to two solids of this type of polar mesogens, rotating at the magic angle, to extract carbon-13 chemical shift anisotropy tensors. They are useful not only to aid 13C peak assignments in the isotropic state, but are necessary for accounting the observed chemical shifts of various carbon sites, resided on the bent-core aromatic part, in the spectrum of an aligned mesophase. An example to extract ordering information is given for one of the studied mesogens.

JMR: Spinevolution software - solution and solids NMR simulations

Journal of Magnetic Resonance
Volume 178, Issue 2 , February 2006, Pages 248-282

SPINEVOLUTION: A powerful tool for the simulation of solid and liquid state NMR experiments

Mikhail Veshtort and Robert G. Griffin

Department of Chemistry, MIT/Harvard Center for Magnetic Resonance, Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Abstract

Exact numerical simulations of NMR experiments are often required for the development of new techniques and for the extraction of structural and dynamic information from the spectra. Simulations of solid-state magic angle spinning (MAS) experiments can be particularly demanding both computationally and in terms of the programming required to carry them out, even if special simulation software is used. We recently developed a number of approaches that dramatically improve the efficiency and allow a high degree of automation of these computations. In the present paper, we describe SPINEVOLUTION, a highly optimized computer program that implements the new methodology. The algorithms used in the program will be described separately. Although particularly efficient for the simulation of experiments with complex pulse sequences and multi-spin systems in solids, SPINEVOLUTION is a versatile and easy to use tool for the simulation and optimization of virtually any NMR experiment. The performance of SPINEVOLUTION was compared with that of another recently developed NMR simulation package, SIMPSON. Benchmarked on a series of examples, SPINEVOLUTION was consistently found to be orders of magnitude faster. At the time of publication, the program is available gratis for non-commercial use.

Keywords: NMR simulations; Virtual NMR spectrometer; Software; Parameter optimization; Data fitting

JMR: Samoson - DOR of half integer quadrupoles

Journal of Magnetic Resonance
Volume 178, Issue 2 , February 2006, Pages 212-219

New opportunities for double rotation NMR of half-integer quadrupolar nuclei

Arno P.M. Kentgens a, Ernst R.H. van Eck, T.G. Ajithkumar, Tiit Anupõld, Jaan Past, Andres Reinhold and Ago Samoson

a Department of Physical Chemistry/Solid-State NMR, Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 1, The Netherlands
b National Institute of Chemical Physics and Biophysics, 12618 Tallinn, Estonia

Abstract

A combined approach is presented which expands the applicability of double rotation (DOR) by overcoming its most prominent disadvantages: spinning stability and sensitivity. A new design using air-bearings for the inner rotor and a computer-assisted start-up procedure allows DOR operation over in principle unlimited time at outer rotor speeds of up to 2000 Hz. Sensitivity enhancement of the DOR experiment is achieved by applying amplitude-modulated adiabatic pulses such as the double frequency sweep (DFS) before pulse excitation. Repeating the DFS enhancement and signal readout several times without allowing for spin–lattice relaxation leads to sensitivity enhancements of a factor 3 for 27Al in various minerals. As a result, it becomes possible to study low sensitivity quadrupolar nuclei and various long duration 2D measurements can be performed routinely. Spinning is adequate to suppress residual homonuclear dipolar couplings in the spectral dimension of typical quadrupolar spin systems. In 2D-exchange spectroscopy, however, homonuclear correlation can still be established through dipolar–quadrupolar cross-terms.

Keywords: DOR; Repetitive DFS; Quadrupolar nuclei; MQDOR; Homonuclear correlation

JMR: Larsen: 47Ti and 49Ti at high fields

Journal of Magnetic Resonance
Volume 178, Issue 2 , February 2006, Pages 228-236

Separation of 47Ti and 49Ti solid-state NMR lineshapes by static QCPMG experiments at multiple fields

Flemming H. Larsen a, Ian Farnan b and Andrew S. Lipton c

aDepartment of Food Science, Quality and Technology, The Royal Veterinary and Agricultural University, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark
bDepartment of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK
cWilliam R. Wiley, Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Mail Stop K8-98 Richland, WA 99352, USA

Received 20 August 2005; revised 1 October 2005. Available online 2 November 2005.

Abstract

Experimental procedures are proposed and demonstrated that separate the spectroscopic contribution from both 47Ti and 49Ti in solid-state nuclear magnetic resonance spectra. These take advantage of the different nuclear spin quantum numbers of these isotopes that lead to different ‘effective’ radiofrequency fields for the central transition nutation frequencies when these nuclei occur in sites with a significant electric field gradient. Numerical simulations and solid-state NMR experiments were performed on the TiO2 polymorphs anatase and rutile. For anatase, the separation of the two isotopes at high field (21.1 T) facilitated accurate determination of the electric field gradient (EFG) and chemical shift anisotropy (CSA) tensors. This was accomplished by taking advantage of the quadrupolar interaction between the EFG at the titanium site and the different magnitudes of the nuclear quadrupole moments (Q) of the two isotopes. Rutile, having a larger quadrupolar coupling constant (CQ), was examined by 49Ti-selective experiments at different magnetic fields to obtain spectra with different scalings of the two anisotropic tensors. A small chemical shielding anisotropy (CSA) of −30 ppm was determined.

Keywords: QCPMG; Solid state; Isotope-selective; Ti; Multiple fields

News reader feed: http://ssnmr.blogspot.com/atom.xml

If you are using a newsreader (RSS) on your computer (e.g., like Sharpreader), you can pick up the feed for this site by adding this link:

http://ssnmr.blogspot.com/atom.xml

Unfortunately, I cannot figure out how to do email notifications, but perhaps this is for the best.

Rob

Review: Mei Hong: Solid-State NMR of membrane proteins

Acc. Chem. Res., ASAP Article 10.1021/ar040037e S0001-4842(04)00037-8
Web Release Date: January 7, 2006

Solid-State NMR Studies of the Structure, Dynamics, and Assembly of -Sheet Membrane Peptides and -Helical Membrane Proteins with Antibiotic Activities

Mei Hong

Department of Chemistry, Iowa State University, Ames, Iowa 50011

Received October 3, 2005

Abstract:

-Sheet antimicrobial peptides and -helical channel-forming colicins are bactericidal molecules that target the lipid membranes of sensitive cells. Understanding the mechanisms of action of these proteins requires knowledge of their three-dimensional structure in the lipid bilayer. Solid-state NMR has been used to determine the conformation, orientation, depth of insertion, oligomerization, mobility, and lipid interaction of these membrane peptides and proteins. We review the NMR methods developed and applied to study the structure and dynamics of these antibiotic membrane proteins. These studies shed light on how these peptides disrupt lipid membranes and provide fundamental insights into the folding of -sheet and -helical membrane proteins.

JACS article: INADEQUATE to map bonding in [Ce@C82]-

J. Am. Chem. Soc., ASAP Article 10.1021/ja055882m S0002-7863(05)05882-8
Web Release Date: January 20, 2006

Copyright © 2006 American Chemical Society

Analysis of Lanthanide-Induced NMR Shifts of the Ce@C₈₂ Anion

Michio Yamada, Takatsugu Wakahara, Yongfu Lian, Takahiro Tsuchiya, Takeshi Akasaka,* Markus Waelchli, Naomi Mizorogi,Shigeru Nagase,* and Karl M. Kadish

Center for Tsukuba Advanced Research Alliance, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan, Bruker Biospin K. K., Tsukuba, Ibaraki 305-0051, Japan, Department of Theoretical Molecular Science, Institute for Molecular Science, Okazaki, Aichi 444-8585, Japan, and University of Houston, Houston, Texas 77204-5003

Abstract:

The mapping of bond connectivity in the carbon cage of [Ce@C₈₂]^- and full assignment of the NMR lines were successfully achieved by means of 2D INADEQUATE NMR measurement. Paramagnetic NMR analysis shows that the Ce atom in [Ce@C₈₂]^- is located at an off-centered position adjacent to a hexagonal ring along the C₂ axis of the C_2v-C₈₂ cage.

JACS article: 35Cl NMR, Bryce

J. Am. Chem. Soc., ASAP Article 10.1021/ja057253i S0002-7863(05)07253-7
Web Release Date: January 19, 2006

Solid-State ^35/37Cl NMR Spectroscopy of Hydrochloride Salts of Amino Acids Implicated in Chloride Ion Transport Channel Selectivity: Opportunities at 900 MHz

David L. Bryce,* Gregory D. Sward, and Samyuktha Adiga

Contribution from the Department of Chemistry, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada

Abstract:

The results of a detailed systematic chlorine solid-state NMR study of several hydrochloride salts of amino acids implicated in chloride ion transport channel selectivity are reported. ³⁵Cl and ³⁷Cl NMR spectra have been obtained for stationary and/or magic-angle spinning powdered samples of the following compounds on 500 and/or 900 MHz spectrometers: DL-arginine HCl monohydrate, L-lysine HCl, L-serine HCl, L-glutamic acid HCl, L-proline HCl, L-isoleucine HCl, L-valine HCl, L-phenylalanine HCl, and glycine HCl. Spectral analyses provide information on the anisotropic properties and relative orientations of the chlorine electric field gradient and chemical shift (CS) tensors, which are intimately related to the local molecular and electronic structure. Data obtained at 900 MHz provide unique examples of the effects of CS anisotropy on the NMR spectrum of a quadrupolar nucleus. The range of chlorine quadrupolar coupling constants (C_Q) measured, -6.42 to 2.03 MHz, demonstrates the sensitivity of this parameter to the chloride ion environment and suggests the applicability of chlorine solid-state NMR as a novel experimental tool for defining chloride binding environments in larger ion channel systems. Salts of hydrophobic amino acids are observed to tend to exhibit larger values of C_Q than salts of hydrophilic amino acids. A simple model for rationalizing the observed trend in C_Q is proposed. For salts for which neutron diffraction structures are available, we identify a quantum chemical method which reproduces experimental values of C_Q^- with a root-mean-square deviation of 0.1 MHz and a correlation coefficient of 0.9998. On the basis of this, chlorine NMR tensors are predicted for the Cl binding site in ClC channels.

ISI Impact Factors 2004

The 2004 ISI impact factors can be found at the following link

http://www.qualitas1998.net/ismn/impact_factors.htm

Crystallographic inequivalence in 13C NMR

Hiyam:
Solid State Nuclear Magnetic Resonance
Volume 29, Issue 4 , June 2006, Pages 283-293

Solid-state NMR and 2,3-dicyano-5,7-dimethyl-6H-1,4-diazepine

Jeffrey M. Njus

Center for Advanced Materials, Department of Chemistry, University of Massachusetts Lowell, Lowell, MA 01854-5046, USA

Abstract

Crystalline 2,3-dicyano-5,7-dimethyl-6H-1,4-diazepine (A) was investigated by solid-state NMR spectroscopy, X-ray diffraction, and spectral simulations. The solid-state 13C NMR spectra of A display peculiar splittings for the methyl and cyano resonances. The crystal structure of A indicates that the methyl doublet is a consequence of two crystallographically inequivalent environments. The methyl motions associated with each site was examined via spin-lattice relaxation time (T1) measurements, and the carbon relaxation times (T1C) were used to calculate energy barriers to methyl rotation. The energy barriers to rotation were then used to correlate each methyl 13C shift with a particular crystallographic environment. The complex cyano splittings, however, are a result of both crystallographic inequivalence and residual 13C–14N dipolar coupling. The multiplet patterns of the isotropic shifts (centerbands) are dependent upon the magic-angle spinning (MAS) rate. Spectral simulations, using the perturbation method, of the centerbands and first-order sidebands were used to demonstrate, and elucidate, the observed MAS rate-dependent multiplet patterns of the cyano signals.

Keywords: Crystallographic inequivalence; Asymmetric unit cell; Spin-lattice relaxation; NOE; Spectral simulations

J. Chan: selective excitation and LG CP/MAS

Solid State Nuclear Magnetic Resonance
Volume 29, Issue 4 , June 2006, Pages 272-277

Spectral editing based on selective excitation and Lee-Goldburg cross-polarization under magic angle spinning

Shing-Jong Huanga, Yao-Hung Tsengb, Yun Moub, Shang-Bin Liua, Shih-Hao Huangc, Chun-Pin Linc and Jerry C.C. Chanb, Corresponding Author Contact Information, E-mail The Corresponding Author

Abstract

We show that a Gaussian-shaped pulse can be used to excite selected 1H signals in hydroxyapatite, monetite and H–Y zeolite loaded with trimethylphosphine oxide (TMPO). This selective excitation method can be incorporated into Lee-Goldburg (LG) cross-polarization to obtain useful spectral editing opportunity. This new strategy has been applied to identify the Brønsted and the Lewis acid sites in H–Y zeolite using TMPO as the probe molecule.

Keywords: MAS; Solid-state NMR; Lee-Goldburg; Zeolite; HY; TMPO; LG-CP

Grant group: 13C CS tensors and powder XRD

Hiyam:

J. Am. Chem. Soc., ASAP Article 10.1021/ja055570j S0002-7863(05)05570-8
Web Release Date: January 12, 2006

Characterizing Challenging Microcrystalline Solids with Solid-State NMR Shift Tensor and Synchrotron X-ray Powder Diffraction Data: Structural Analysis of Ambuic Acid

James K. Harper, David M. Grant,* Yuegang Zhang, Peter L. Lee, and Robert Von Dreele

Contribution from the Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112, and Argonne National Laboratory, Advanced Photon Source, Argonne, Illinois 60439

Synchrotron X-ray powder diffraction and solid-state 13C NMR shift tensor data are combined to provide a unique path to structure in microcrystalline organic solids. Analysis is demonstrated on ambuic acid powder, a widely occurring natural product, to provide the complete crystal structure. The NMR data verify phase purity, specify one molecule per asymmetric unit, and provide an initial structural model including relative stereochemistry and molecular conformation. A refinement of X-ray data from the initial model establishes that ambuic acid crystallizes in the P21 space group with unit cell parameters a = 15.5047(7), b = 4.3904(2), and c = 14.1933(4) Å and = 110.3134(3). This combined analysis yields structural improvements at two dihedral angles over prior NMR predictions with differences of 103 and 37 found. Only minor differences of ±5.5, on average, are observed at all remaining dihedral angles. Predicted hydroxyl hydrogen-bonding orientations also fit NMR predictions within ±6.9. This refinement corrects chemical shift assignments at two carbons and reduces the NMR error by ~16%. This work demonstrates that the combination of long-range order information from synchrotron powder diffraction data together with the accurate shorter range structure given by solid-state NMR measurements is a powerful tool for studying challenging organic solids.

17O NMR from the Warwick group in J. Phys. Chem. A

Cory, please have a look:

Experimental and Theoretical 17O NMR Study of the Influence of Hydrogen-Bonding on C=O and O-H Oxygens in Carboxylic Solids

Alan Wong, Kevin J. Pike, Rob Jenkins, Guy J. Clarkson, Tiit Anupõld, Andrew P. Howes, David H. G. Crout, Ago Samoson, Ray Dupree, and Mark E. Smith*

In Final Form: December 1, 2005

Abstract:
A systematic solid-state 17O NMR study of a series of carboxylic compounds, maleic acid, chloromaleic acid, KH maleate, KH chloromaleate, K2 chloromaleate, and LiH phthalate·MeOH, is reported. Magic-angle spinning (MAS), triple-quantum (3Q) MAS, and double angle rotation (DOR) 17O NMR spectra were recorded at high magnetic fields (14.1 and 18.8 T). 17O MAS NMR for metal-free carboxylic acids and metal-containing carboxylic salts show featured spectra and demonstrate that this combined, where necessary, with DOR and 3QMAS, can yield site-specific information for samples containing multiple oxygen sites. In addition to 17O NMR spectroscopy, extensive quantum mechanical calculations were carried out to explore the influence of hydrogen bonding at these oxygen sites. B3LYP/6-311G++(d,p) calculations of 17O NMR parameters yielded good agreement with the experimental values. Linear correlations are observed between the calculated 17O NMR parameters and the hydrogen bond strengths, suggesting the possibility of estimating H-bonding information from 17O NMR data. The calculations also revealed intermolecular H-bond effects on the 17O NMR shielding tensors. It is found that the S11 and S22 components of the chemical shift tensor at O-H and C=O, respectively, are aligned nearly parallel with the strong H-bond and shift away from this direction as the H-bond interaction weakens.

Organometallics, 24 (26), 6319 -6330, 2005

Ab Initio and DFT Study of the 29Si NMR Chemical Shifts in RSiSiR

Miriam Karni and Yitzhak Apeloig, Nozomi Takagi and Shigeru Nagase

Abstract:
The syntheses of the first two disilynes were reported recently: the first by Wiberg and co-workers, who synthesized RSiSiR (1; R = SiMe(Si-t-Bu3)2), and the second by Sekiguchi and co-workers, who synthesized RSiSiR (2; R = Si-i-Pr[CH(SiMe3)2]2), which was also characterized by X-ray crystallography and NMR spectroscopy. We report the first detailed quantum-mechanical study of the 29Si NMR chemical shifts of disilynes, RSiSiR, in particular those with R = H, CH3, SiH3, SiMe(SiH3)2, SiMe(SiMe3)2, SiMe(Si-t-Bu3)2 (1), Si-i-Pr[CH(SiMe3)2]2 (2). The main conclusions are as follows: (1) Small changes in geometry (i.e., in r(SiSi), in the RSiSi bond angle, and in the RSiSiR torsion angle) strongly affect the chemical shift. (2) (29Si) values of the triply bonded silicon atoms in RSiSiR (R = H, SiH3) are -26 and 68 ppm, respectively (at MP2/6-311G(3d)//B3LYP/6-31G(d,p)), reflecting a significant effect of the silyl substituent. (3) (29Si) values calculated using the HCTH407 GGA functional are in excellent agreement with those calculated at the MP2 and CCSD levels of theory for model disilynes and with experimental chemical shifts measured for disilenes. This is therefore our recommended method for calculating (29Si) values of disilynes, especially with large substituents. A poorer agreement is observed when applying the commonly used hybrid B3LYP functional. (4) The calculated chemical shift of the triply bonded silicon atoms in 1 is in the range of 88 ± 5 ppm, in good agreement with the observed chemical shift of the product obtained by Wiberg, supporting his assignment. (5) The calculated (29Si) value in 2 is ca. 60 ppm, considerably upfield from the experimental chemical shift of 89.9 ppm (in solution), raising the possibility that the structure of 2 in solution is slightly different from that in the solid state.

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Chem Comm: SSNMR of paramagnetic Cu(I)/Cu(II)/Zn(II) coordination polymer

Chemical Communications, 2006, (Advance Article) DOI: 10.1039/b512430a A paramagnetic Cu(I)/Cu(II)/Zn(II) coordination polymer with multiple CN-binding modes and its solid-state NMR characterization Liang Ouyang, Pedro M. Aguiar, Raymond J. Batchelor, Scott Kroeker and Daniel B. Leznoff A Cu(I)/Cu(II)/Zn(II) mixed-valent [Cu(en)2][Zn(NC)4(CuCN)2] polymer, which has a 2-D layer structure with six structurally inequivalent cyanides in four distinct bonding modes, has been prepared; structurally informative 13C and 15N MAS NMR spectra of this paramagnetic system are readily observable.

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The Journal of Chemical Physics. Chem. Phys. 123, 244505 PDF (223 kB)

Theoretical prediction of the coordination number, local composition, and pressure-volume-temperature properties of square-well and square-shoulder fluids
Jiawen Hu, Zhenhao Duan

By assuming a Boltzmann distribution for the molecular equilibrium between local and bulk environments, a general model is derived for the prediction of coordination numbers and local compositions of square-well and square-shoulder fluids. The model has no empirical parameter fitted from the data of square-well and square-shoulder fluids, but is valid from the low-density limit to the high-density limit. The applicable width of well or shoulder covers the commonly used range varying from 1.0 to 2.0. The model can accurately predict the coordination numbers of pure square-well and square-shoulder fluids, so the equation of state derived from it is superior to other equations of state based on the existing coordination number models. The model also accurately predicts the local compositions of mixtures in wide ranges of density and size ratio (1.0–8.0), as well as the configuration energy of lattice gases and highly nonideal lattice mixtures. It is remarkable that the model correctly predicts temperature-dependent coordination numbers and local compositions for both equal- and unequal-sized mixtures at close packing, which cannot be predicted by the existing coordination number models. Our derivation demonstrates that the energy parameters in local composition models should represent the potential difference of a molecule between the local and bulk environments, not the pair-interaction potential, and depend on the system conditions and different kinds of pair-interaction parameters. This result is very useful for the development of local composition and activity coefficient models and the mixing rules of equations of state. ©2005 American Institute of Physics